Exhaust gas driven turbochargers include a rotating shaft carrying a turbine wheel and a compressor wheel, which is rotatably supported within a center housing by one or more lubricated bearings (e.g., oil lubricated). During operation, exhaust gas from an internal combustion engine drives a turbocharger's turbine wheel, which, in turn, drives the compressor wheel to boost charge air to the internal combustion engine. Through proper bearing lubrication, a turbocharger's rotating assembly can readily withstand rotational speeds in excess of 100,000 rpm.
Leakage of bearing lubricant can cause some problems. For example, at the turbine end, lubricant can enter the exhaust stream and thereby affect emissions and/or after-treatment technology. At the compressor end, lubricant can enter the intake stream and enter the engine and/or foul component such as an inter-cooler's heat exchange surface.
In some instances, a bearing provides one or more thrust surfaces for axial loads. For example, axial loading of a rotating assembly may cause a surface of an integral shaft and turbine wheel to approach a surface of a bearing. In general, clearances and lubricant create a protective layer such that loads may be transferred without such surfaces contacting. However, for some operational conditions, axial loading may cause the lubricant layer to diminish and hence lose its protective effect. Various exemplary technologies described herein can address such lubrication leakage and/or loading issues.